Device and method for producing an encoded audio and/or video data stream

ABSTRACT

An apparatus for generating an encrypted data stream representing an audio and/or video signal comprises an encoder for encoding an input signal to generate a data stream with a predefined data stream syntax as output signal. The apparatus further comprises an encryption means coupled with the decoder in order to influence encoder internal data and/or the output signal of the encoder in a uniquely reversible manner based on a key such that the generated encrypted data stream comprises payload information differing from payload information of a data stream that would be generated by the apparatus without the presence of an encryption means and that the generated encrypted data stream comprises the predefined data stream syntax. Thereby, a flexible data stream encryption is achieved, wherein the degree of encryption can be freely selected such that the owner of a decoder who does not possess the key, still obtains a rough idea of the audio and/or video signal which might cause him to buy the key in order to hear or view the audio and/or video signal in its full quality. The encoder-specific encryption and decryption concept can be implemented into already existing encoders/decoders with little effort.

FIELD OF THE INVENTION

The present invention relates to the encryption and decryption of audioand/or video signals and, in particular, to a flexible concept forcustom-selective provision of audio and/or video signals.

BACKGROUND OF THE INVENTION AND PRIOR ART

With the widespread availability of the Internet in connection withhearing-adapted audio encoding methods, a simple worldwide distributionof high-quality audio signals has become possible. In particular, thishas lead to a worldwide wave of music piracy, wherein people for exampleencode purchased CD music according to the standard MPEG layer-3 (MP3)and place it illegally on the World Wide Web (WWW). According toestimates, about 10 million downloads of music is exchanged in a day,without the holders of the corresponding copies and license rightshaving authorised same or having received the respective paymentstherefore. This has lead to great concern in the music industry.

Nowadays, there are, in particular, many constrains concerning thesituation of music distribution. Firstly, a wide spread know-howconcerning the audio compression technology exists, manifested, forexample, in the standard MPEG layer-3 (MP3). Additionally, softwareencoders, software decoders and MP3-players (for example, mp3enc, 13enc,WinPlay3) and other formats run on a number of operating systems,including the Windows operating system. Furthermore, many Internetlocations exist offering MP3-music that has often been placed therewithout authorisation.

Apart from the software encoders and decoders, hardware players exist aswell, for example, MPLayer3, MP-Man, Rio, etc., that are able to playMP3 pieces that have either been encoded from a CD or are files thathave been downloaded from the Internet. These players have, so far, noimplemented protection techniques for enforcing copy or license rights.Additionally, devices for writing to CD-ROMs exist that are able towrite to audio CDs and MP3 CD-ROMs. Meanwhile, these devices are offeredto prices that have lead to a wide spread availability. Furthermore, theprices for high-volume hard discs have fallen, which is why mostInternet participants have almost unlimited memory capacities. Finally,we want to point out the tendency that transmission costs for files keepfalling.

While in the above hardware players no protection techniques have beenimplemented, there are still several techniques for protecting audioand/or video data (i.e. multimedia data, naming, for example, themultimedia protection protocol MMP. This technology represents aso-called “Secure Envelope” technique.

DE 196 25 625 C1 describes such a technique for encrypting anddecrypting of multimedia data. Data encoded according to an audio orvideo standard are encrypted at least partly via, for example, a DESencryption method (DES=Data Encryption Standard) and written into apayload data block.

The payload data block is provided with a determination data blockcomprising, apart from a plurality of further information, alsoinformation concerning the encryption algorithm used with the encryptionas well as the key needed therefore. The key comprises user informationsuch that only a specific user who is authorised for playing a piece ofmultimedia, for example, by purchase or licensing can decrypt the piece.A player that does not have the correct key will stop operating as soonas it encounters the encrypted multimedia data. Thereby, the objectivethat only the authorised user can play a piece of multimedia isachieved. This Secure Envelope technique therefore represents a twolevel method wherein a piece of multimedia is encoded first in order toobtain a significant data compression and wherein then a cryptographicalalgorithm is used in order to defend the encoded piece of multimediaagainst unauthorised attackers.

For applications that do not require such maximum protection, thedescribed concept is disadvantageously in that it can become relativelyexpensive and can require significant modifications to players in orderto be able to process the determination data block. The players that aremass products in the consumer area after all, and therefore have to beoffered inexpensively should, however, if possible, not having to bechanged at all in order to be able to play protected pieces ofmultimedia. Thus, it has to be noted that the known encryption conceptmakes a maximum protection and a high encryption flexibility possible byrespectively designing the start block, but that, however, distinctivechanges with the players are necessary in order to decrypt encryptedfiles or to read them at all.

U.S. Pat. No. 5,796,838 discloses a method and an apparatus for carryingout an inversion of a frequency spectrum. The inversion of the frequencyspectrum is achieved by converting a non-encrypted audio signal fromanalog to digital. The audio signal is then subjected to a positivecomplex frequency translation such that the negative frequencycomponents of the audio signal will be positioned at around 0 Hz. Theaudio signal converted regarding to its frequency will then be low-passfiltered, so that only the base band components are left. The filteredcomplex base band signal will then be subjected to an arbitrary complexfrequency displacement in order to position the signal frequency in adesired frequency band. The resulting signal has an inverted spectrumrelative to the original audio signal. Extracting the real part of thecomplex samples will generate the final audio signal.

U.S. Pat. No. 4,534,037 discloses a method and an apparatus for ascrambled pulse code modulation transmission or recording. In order toemphasise special spectral components of a sequence of digital signalsthat have been transmitted or recorded in pulse code words, “repacked”words are established comprising one or several bits of a word of theoriginal sequence and a complementary number of bits of the followingword. The bits of a word out of which a “repacked” word consists of willbe inverted prior to repacking such that, for example, the fourfoldsampling frequency, the double sampling frequency or the samplingfrequency itself can be emphasised in the spectrum. It is possible totransform the frequency spectrum downward regarding to the frequencywithout inversion of words.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a different conceptfor decrypting and encrypting audio and/or video signals, respectively.

In accordance with a first aspect of the present invention, this objectis achieved by an apparatus for generating an encrypted data stream froman audio signal, comprising: an encoder for encoding the audio signal inorder to generate a data stream with a predefined data stream syntax asoutput signal; an encryption means coupled with the encoder forinfluencing encoder internal data in a uniquely reversible manner basedon a key such that the generated encrypted data stream comprises payloadinformation differing from payload information of a data stream thatwould be generated by the apparatus without the presence of theencryption means and that the generated encrypted data stream comprisesthe predefined data stream syntax, wherein said encoder is an encoderfor audio signals, comprising: an analysis filter bank for convertingthe audio signal from the time domain into a spectral representation inorder to obtain spectral values; a quantizing means for quantizing thespectral values under consideration of a psychoacoustic model; and anentropy encoder arranged to carry out an entropy encoding of thequantized spectral values via a plurality of predefined code tableswherein each code table for the entropy encoding of quantized spectralvalues is provided in a frequency band and wherein at least onefrequency band comprises two or more quantized spectral values, andwherein said encryption means is arranged to resort the two or morequantized spectral values in the frequency band comprising two or morequantized spectral values having an associated code table based on thekey.

In accordance with a second aspect of the present invention, this objectis achieved by an apparatus for generating a data stream encrypted basedon a second key from a first data stream encrypted based on a first key,wherein said first data stream is an audio signal encoded by using anencoder with a predefined data stream syntax, wherein said first datastream is encrypted such that that two or more quantized spectral valuesin a frequency band comprising two or more quantized spectral values andhaving an associated code table have been resorted based on the firstkey, wherein after the resorting an entropy encoding of the quantizedspectral values has been carried out via a plurality of predefined codetables, wherein each code table is provided for the entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,comprising: a partial decoder for reversing part of the encoding suchthat the resorted two or more spectral values are present; a decryptionmeans for decrypting the resorted two or more spectral values byreversing the resorting based on the first key; an encryption means forinfluencing the sequence of the two or more spectral values of thefrequency band that has an associated code table based on the secondkey; a partial encoder for carrying out part of the encoding that hasbeen reversed by the partial decoder in order to generate the datastream encrypted based on the second key, wherein the second data streamhas the predefined data stream syntax.

In accordance with a third aspect of the present invention, this objectis achieved by an apparatus for generating a second data streamencrypted based on a key from a data stream, wherein said first datastream is an audio signal encoded using an encoder with a predefineddata stream syntax, comprising: a partial decoder for reversing part ofthe encoding such that quantized spectral values of the audio signal arepresent; an encryption means for resorting two or more quantizedspectral values in a frequency band comprising two or more spectralvalues based on the first key, wherein one of a plurality of predefinedcode tables is associated to the frequency band for the entropyencoding, wherein each code table is provided for an entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,wherein the encryption means is arranged to resort the quantizedspectral values that have the same associated code table; a partialencoder for carrying out part of the encoding that has been reversed bythe partial decoder in order to generate the data stream encrypted basedon the key, wherein the second data stream has the predefined datastream syntax.

In accordance with a fourth aspect of the present invention, this objectis achieved by an apparatus for generating a decrypted data stream froma first data stream encrypted based on a key, wherein said first datastream is an audio signal with a predefined data stream syntax encodedby using an encoder, wherein said first data stream is encrypted suchthat at least two or more quantized spectral values in a frequency bandhave been resorted based on the first key wherein a plurality ofpredefined code tables for an entropy encoding is associated with thefrequency band whose quantized spectral values have been resorted,wherein each code table for the entropy encoding is provided for theentropy encoding of quantized spectral values in a frequency band andwherein at least one frequency band comprises the two or more quantizedspectral values, comprising: a partial decoder for reversing part of theencoding such that the resorted two or more quantized spectral valuesare present, wherein the resorted two or more quantized spectral valuesbelong to a frequency band that has an associated code table; adecryption means for decrypting the resorted two or more quantizedspectral values by reversing the resorting based on the key; a partialencoder for carrying out part of the encoding that has been reversed bythe partial decoder in order to generate the second data stream with thepredefined data stream syntax.

In accordance with a fifth aspect of the present invention, this objectis achieved by an apparatus for generating a decrypted audio signal froman encrypted data stream comprising quantized spectral values of anaudio signal being resorted and afterwards entropy encoded within afrequency band in a uniquely reversible manner, wherein the frequencyband is defined that it has an associated code table from a plurality ofcode tables for the entropy encoding, wherein the encrypted data streamcomprises payload information differing from payload information of anon-encrypted data stream and wherein said encrypted data streamcomprises the same data stream syntax as a non-encrypted data stream,comprising: a decoder for decoding input data in order to generatedecoded output data, wherein the decoder comprises an entropy decoderfor reversing the entropy encoding in order to obtain the resortedquantized spectral values; and a decryption means for influencing theresorted spectral values based on a key in order to reverse the uniquelyreversible resorting which has been carried out in an apparatus forgenerating an encrypted data stream in order to obtain the decryptedaudio and/or video signal.

In accordance with a sixth aspect of the present invention, this objectis achieved by a method for generating an encrypted data stream from anaudio signal, comprising: encoding the audio signal in order to generatea data stream with a predefined data stream syntax as output signal;encrypting encoder internal data by influencing the same in a uniquelyreversible manner based on a key such that the generated encrypted datastream comprises payload information differing from payload informationof a data stream that would be generated without the step of encryptingand that the generated encrypted data stream comprises the predefineddata stream syntax, wherein in the step of encoding an audio signal isencoded, comprising: converting the audio signal from the time domaininto a spectral representation in order to obtain spectral values;quantizing the spectral values under consideration of a psychoacousticmodel; and entropy encoding of the spectral values via a plurality ofpredefined code tables wherein each code table for the entropy encodingof quantized spectral values is provided in a frequency band and whereinat least one frequency band comprises two or more quantized spectralvalues, and wherein said step of encrypting is carried out to resort thetwo or more quantized spectral values in the frequency band comprisingtwo or more quantized spectral values having an associated code tablebased on the key.

In accordance with a seventh aspect of the present invention, thisobject is achieved by a method for generating a second data streamencrypted based on a second key from a first data stream encrypted basedon a first key, wherein said first data stream is an audio signal with apredefined data stream syntax encoded by using an encoder, wherein saidfirst data stream is encrypted such that two or more quantized spectralvalues in a frequency band comprising two or more quantized spectralvalues and having an associated code table have been resorted based onthe first key, wherein after the resorting an entropy encoding of thequantized spectral values has been carried out via a plurality ofpredefined code tables, wherein each code table is provided for theentropy encoding of quantized spectral values in a frequency band andwherein at least one frequency band comprises the two or more quantizedspectral values, comprising: reversing part of the encoding such thatthe resorted two or more spectral values are present; decrypting theresorted two or more spectral values by reversing the resorting based onthe first key; encrypting by influencing the sequence of the two or morespectral values of the frequency band that has an associated code tablebased on the second key; carrying out the part of the encoding that hasbeen reversed by the step of reversing in order to generate the datastream encrypted based on the second key, wherein the second data streamhas the predefined data stream syntax.

In accordance with an eighth aspect of the present invention, thisobject is achieved by a method for generating a second data streamencrypted based on a key from a first data stream, wherein said firstdata stream is an audio signal with a predefined data stream syntaxencoded by using an encoder, comprising: reversing part of the encodingsuch that quantized spectral values of the audio signal are present;encrypting by resorting two or more quantized spectral values in afrequency band comprising two or more spectral values based on the firstkey, wherein one of a plurality of predefined code tables is associatedto the frequency band for the entropy encoding, wherein each code tableis provided for an entropy encoding of quantized spectral values in afrequency band and wherein at least one frequency band comprises the twoor more quantized spectral values, wherein the encryption means isarranged to resort the quantized spectral values that have the sameassociated code table; carrying out part of the encoding that has beenreversed by the partial decoder in order to generate the data streamencrypted based on the key, wherein the second data stream has thepredefined data stream syntax.

In accordance with a ninth aspect of the present invention, this objectis achieved by a method for generating a decrypted data stream from afirst data stream encrypted based on a key, wherein said first datastream is an audio signal with a predefined data stream syntax encodedby using an encoder, wherein said first data stream is encrypted suchthat at least two or more quantized spectral values in a frequency bandhave been resorted based on the first key, wherein a plurality ofpredefined code tables for an entropy encoding is associated with thefrequency band whose quantized spectral values have been resorted,wherein each code table for the entropy encoding of quantized spectralvalues is provided in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,comprising: reversing part of the encoding such that the resorted two ormore quantized spectral values are present, wherein the resorted two ormore quantized spectral values belong to the frequency band that has anassociated code table; decrypting the resorted two or more quantizedspectral values by reversing the resorting based on the key; carryingout part of the encoding that has been reversed by the step of reversingin order to generate the second data stream with the predefined datastream syntax.

In accordance with a tenth aspect of the present invention, this objectis achieved by a method for generating a decrypted audio signal from anencrypted data stream comprising quantized spectral values of an audiosignal being resorted and afterwards entropy encoded within a frequencyband in a uniquely reversible manner, wherein the frequency band isdefined by having an associated code table from a plurality of codetables for the entropy encoding wherein the encrypted data streamcomprises payload data differing from payload data of a non-encrypteddata stream and wherein the encrypted data stream comprises the samedata stream syntax as a non-encrypted data stream, comprising: decodinginput data in order to generate decoded output data, wherein in the stepof decoding an entropy encoding for reversing the entropy encoding iscarried out in order to obtain the resorted quantized spectral values;and decrypting by influencing the resorted quantized spectral valuesbased on a key in order to reverse the uniquely reversible resortingthat has been carried out by generating an encrypted data stream inorder to obtain the decrypted audio signal.

In accordance with an eleventh sixth aspect of the present invention,this object is achieved by an apparatus for generating an encrypted datastream from an audio signal, comprising: an encoder for encoding theaudio signal in order to generate a data stream with a predefined datastream syntax as output signal; an encryption means coupled with theencoder for influencing encoder internal data of the encoder in auniquely reversible manner based on a key such that the generatedencrypted data stream comprises payload information differing frompayload information of a data stream that would be generated by theapparatus without the presence of the encryption means and that thegenerated encrypted data stream comprises the predefined data streamsyntax, wherein said encoder is an encoder for audio signals,comprising: an analysis filter bank for converting the audio signal fromthe time domain into a spectral representation in order to obtainspectral values; a quantizing means for quantizing the spectral valuesunder consideration of a psychoacoustic model; and an entropy encoderarranged to carry out an entropy encoding of the spectral values inorder to obtain a sequence of code words wherein the sequence of codewords represents an entropy encoded version of the audio signal, andwherein said encryption means is arranged to resort the sequence of codewords by changing an order of code words based on the key.

In accordance with a twelfth aspect of the present invention, thisobject is achieved by an apparatus for generating a data streamencrypted based on a second key from a first data stream encrypted basedon a first key, wherein said first data stream is an audio signal with apredefined data stream syntax encoded using an encoder, wherein saidfirst data stream is encoded such that a sequence of code wordsgenerated by entropy encoding of quantized spectral values has beenresorted by changing an order of code words based on the first key,comprising: a partial decoder for reversing part of the encoding suchthat the resorted sequence of code words is present; a decryption meansfor reversing the resorting based on the first key; an encryption meansfor resorting the sequence of code words based on the second key bychanging an order of code words; a partial encoder for carrying out partof the encoding that has been reversed by the partial decoder in orderto generate the data stream encrypted based on the second key, whereinthe second data stream has the predefined data stream syntax.

In accordance with a thirteenth aspect of the present invention, thisobject is achieved by an apparatus for generating a second data streamencrypted based on a key from a first data stream, wherein said firstdata stream is an audio signal with a predefined data stream syntaxencoded by using an encoder, comprising: a partial decoder for reversingpart of the encoding such that a sequence of code words generated byentropy encoding of quantized spectral values is present; an encryptionmeans for resorting the sequence of code words based on the key bychanging an order of code words; a partial encoder for carrying out partof the encoding that has been reversed by the partial decoder in orderto generate the data stream encrypted based on the key, wherein thesecond data stream has the predefined data stream syntax.

In accordance with a fourteenth aspect of the present invention, thisobject is achieved by an apparatus for generating a decrypted datastream from a first data stream encrypted based on a key, wherein saidfirst data stream is an audio signal with a predefined data streamsyntax encoded by using an encoder, wherein said first data stream isencrypted such that a sequence of code words generated by entropyencoding of quantized spectral values has been resorted by changing anorder of code words based on the first key, comprising: a partialdecoder for reversing part of the encoding such that the resortedsequence of code words is present; a decryption means for reversing theresorting of the sequence of code words based on the key; a partialencoder for carrying out part of the encoding that has been reversed bythe partial decoder in order to generate the second data stream with thepredefined data stream syntax.

In accordance with a fifteenth aspect of the present invention, thisobject is achieved by an apparatus for generating a decrypted audiosignal from an encrypted data stream comprising a sequence of code wordsgenerated by entropy encoding of quantized spectral values resorted in auniquely reversible manner by changing an order of the code wordswherein the encrypted data stream comprises payload data differing frompayload data of a non-encrypted data stream and wherein the encrypteddata stream comprises the same data stream syntax as a non-encrypteddata stream, comprising: a decoder for decoding input data in order togenerate decoded output data; and a decryption means for influencing theresorted sequence of code words based on a key in order to reverse theresorting that has been carried out in an apparatus for generating anencrypted data stream in order to obtain the decrypted audio signal.

In accordance with a sixteenth aspect of the present invention, thisobject is achieved by a method for generating an encrypted data streamfrom an audio signal, comprising: encoding the audio signal in order togenerate a data stream with a predefined data stream syntax as outputsignal; encrypting by influencing encoder internal data in the step ofencoding in a uniquely reversible manner based on a key such that thegenerated encrypted data stream comprises payload information differingfrom payload information of a data stream that would be generated by theapparatus without the presence of the encryption means and that thegenerated encrypted data stream comprises the predefined data streamsyntax, wherein the step of encoding comprises: converting the audiosignal from the time domain into a spectral representation in order toobtain spectral values; quantizing the spectral values underconsideration of a psychoacoustic model; and entropy encoding thespectral values in order to obtain a sequence of code words wherein thesequence of code words represents an entropy encoded version of theaudio signal, and wherein in said step of encrypting based on the keythe sequence of code words is resorted by changing an order of codewords.

In accordance with a seventeenth aspect of the present invention, thisobject is achieved by a method for generating a data stream encryptedbased on a second key from a first data stream encrypted based on afirst key, wherein said first data stream is an encoded audio signalwith a predefined data stream syntax, wherein said first data stream isencrypted such that a sequence of code words generated by entropyencoding quantized spectral values has been resorted by changing anorder of code words based on the first key, comprising: reversing partof the encoding such that the resorted sequence of code words ispresent; reversing the resorting based on the first key; decrypting byresorting the sequence of code words based on the second key; carryingout part of the encoding that has been reversed in the step of reversingin order to generate the data stream encrypted based on the second key,wherein the second data stream has the predefined data stream syntax.

In accordance with an eighteenth aspect of the present invention, thisobject is achieved by a method for generating a second data streamencrypted based on a key from a first data stream, wherein said firstdata stream is an audio signal encoded using an encoder with apredefined data stream syntax, comprising: reversing part of theencoding such that a sequence of code words generated by entropyencoding of spectral values is present; encrypting by resorting thesequence of code words based on the key by changing an order of codewords; carrying out part of the encoding that has been reversed by thestep of reversing in order to generate the data stream encrypted basedon the key, wherein said second data stream has the predefined datastream syntax.

In accordance with a nineteenth aspect of the present invention, thisobject is achieved by a method for generating a decrypted data streamfrom a first data stream encrypted based on a key, wherein said firstdata stream is an encoded audio signal with a predefined data streamsyntax, wherein said first data stream is encrypted such that a sequenceof code words generated by entropy encoding spectral values has beenresorted based by changing an order of code words on a first key,comprising: reversing part of the encoding such that the resortedsequence of code words is present; decrypting by reversing the resortingof the sequence of code words based on the key; carrying out part of theencoding that has been reversed by the step of reversing in order togenerate the second data stream with the predefined data stream syntax.

In accordance with a twentieth aspect of the present invention, thisobject is achieved by an a method for generating a decrypted audiosignal from an encrypted data stream comprising a sequence of code wordsgenerated by entropy encoding quantized spectral values resorted bychanging an order of code words in a uniquely reversible way wherein theencrypted data stream comprises payload data differing from payload dataof a non-encrypted data stream and wherein the encrypted data streamcomprises the same data stream syntax as a non-encrypted data stream,comprising: decoding input data in order to generate decoded outputdata; and decrypting by influencing the resorted sequence of code wordsbased on a key in order to reverse the resorting that has been carriedout in generating an encrypted data stream in order to obtain thedecrypted audio signal.

The present invention is based on the knowledge that for the purpose ofa flexible encryption or decryption, the “Secure Envelope” concept canbe digressed and that a so-called “Soft Envelope” concept can serve tomanage with very limited changes to already existing players. This hasthe advantage that the investments for new developments needed forsufficient encryption can be kept low. This is not achieved by employingan all-purpose encryption method that is applicable for any type ofdata, but by employing a special purpose encryption that is adapted forthe specific encoder or decoder. Especially with highly-compressingencoding methods like, for example, procedures according to the standardMPEG-1 and MPEG-2 including MPEG-2 AAC, so many changes are carried outat the data to be compressed that even small changes to internal data ofthe encoder and/or to the output data of the encoder are enough to, atleast, introduce a (reversible) quality deterioration of the audioand/or video signal at the output of an decoder that does not have anyknowledge about the changes introduced in the encoder, whereby a “soft”encryption is achieved. According to the invention, only such changesare carried out that do not change the data stream syntax of theencoder. Thereby, an inventively encrypted data stream can easily beread-in by a decoder and decoded. Without knowledge about the ways ofthe encryption, i.e., without knowledge about the key the decoded outputsignal will then have a low quality.

The significant advantage of the inventive concept is therefore that bythe manner of intervening with the encoder internal data and/or with theoutput data of the encoder, a very easy encryption can be implemented,the same way as a very strong encryption wherein the output signal of anon-authorised decoder has hardly any similarity with the originalsignal at the input of the encoder. In comparison with all-purposeencryption methods, it is a significant advantage of the presentinvention that the apparatus for generating an encrypted data streamdoes not change the data stream syntax determined by the encoder.Thereby, no significant modifications are required at a decoder that is,as already mentioned, a mass article and has to be inexpensive andcheap.

According to a preferred embodiment of the present invention, theinfluencing of the encoder internal data and/or the output data of theencoder are carried out by an encryption means, merely so intensive thata non-authorised decoder still provides output signals with a certainaudio and/or video quality. Thereby, a user of a non-authorised decodercan, at least, obtain a rough impression of the encrypted music whatmight bring him to buy an authorised version, i.e., the key, in order toreverse the influencing of the data that has been carried out in theapparatus for generating the encrypted data stream in an apparatus forgenerating a decrypted data stream in order to obtain full audio and/orvideo quality.

Another significant advantage of the present invention is that it ispossible to encrypt audio and/or video signals in such a way that theencrypted data stream has exactly the same length as the non-encryptedand merely encoded data stream. If an encoder is implemented in such away that it provides a data rate that corresponds, for example, exactlyto the maximum data rate of an ISDN telephone line, a real timetransmission of the encoded non-encrypted data stream becomes possible.If an encryption method generated a longer data stream, a real timetransmission over this ISDN line would not be possible.

Therefore, the present invention provides an encryption or decryptionconcept wherein the data stream syntax determined by the encoder is notchanged anywhere. For this reason, such an encryption or decryptionconcept provides a maximum flexibility, since a decoder can alwaysdecode an encrypted data stream based on the maintained data streamsyntax. However, dependent on the data influencing in the decryptionmeans, only a very light or a very strong encryption can be achieved insuch a way that a non-authorised listener can either get a relativelygood impression of the encrypted data or a very bad or no impression atall of the encrypted data. Based on the fact that the data stream syntaxpredefined by the encoder is not touched by the encryption, noparticularly large changes to existing players, i.e., decoders, arenecessary in order to be able to implement the inventive concept. Thisproperty is significant, since a multimedia data protection concept,i.e., a protection concept for audio and/or video data, will only findacceptance at the market if it can be implemented without significantcost and is easy to operate.

Finally, the inventive concept has commercial appeal, since all existingdecoders can be used for decoding, which is why users of existingdecoders can listen to encrypted pieces with reduced quality and canthereby perhaps be motivated for the purchase of the key or thepurchase/the licensing of an inventive apparatus for generating adecrypted data stream in order to be able to enjoy the full audio and/orvideo quality.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be discussed indetail below with reference to the accompanying drawings. They show:

FIG. 1 a schematic block diagram of an inventive apparatus forgenerating an encrypted data stream from an audio and/or video signal;

FIG. 2 a schematic block diagram of an inventive apparatus forgenerating an audio and/or video signal as decrypted data stream;

FIG. 3 an embodiment of an inventive apparatus for generating anencrypted data stream comprising an audio decoder according to thestandard MPEG layer-3 or MPEG-2 AAC;

FIG. 4 an apparatus for generating an encrypted data stream according toa further embodiment of the present invention comprising an audioencoder according to the standard MPEG layer-3 or the standard MPEG-2AAC;

FIG. 5 an apparatus for generating a decrypted audio and/or video signalaccording to a further embodiment of the present invention that iscomplementary to the apparatus for generating an encrypted data streamof FIG. 3;

FIG. 6 an apparatus for generating a decrypted audio and/or video signalaccording to a further embodiment of the present invention that iscomplementary to the apparatus for generating an encrypted data streamof FIG. 4;

FIG. 7 an apparatus for generating an encrypted data stream according toa further embodiment of the present invention in order to convert a datastream encrypted with a first key into a data stream encrypted with asecond key;

FIG. 8 an apparatus for generating an encrypted data stream according toa further embodiment of the present invention in order to convert anencoded/non-encrypted data stream into an encoded/encrypted data stream;

FIG. 9 an apparatus for generating an decrypted data stream according toa further embodiment of the present invention in order to convert andencoded/encrypted data stream into an encoded/non-encrypted data stream;

FIG. 10 a schematic block circuit diagram of a known audio encoder, forexample, according to the standard MPEG layer-3 or according to thestandard MPEG-2 AAC; and

FIG. 11 a schematic block circuit diagram of a known audio decoderaccording to the standard MPEG layer-3 or according to the standardMPEG-2 AAC.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a general block circuit diagram of an inventive apparatus10 for generating an encrypted data stream representing an audio and/orvideo signal. The apparatus 10 comprises an input 12 and an output 14.An encoder 16 is connected between the input 12 and the output 14 and iscoupled with an encryption means 18 in order to provide an encrypteddata stream at the output of the apparatus 10 for generating anencrypted data stream, having the same data stream syntax as determinedor demanded by the encoder 16.

The encryption means 18 and the encoder 16 are coupled in such a waythat the encryption means 18 influences encoder internal data (branch 20a) and/or output data of the encoder (branch 20 b), however, it merelyinfluences them in such a way that the data stream syntax of the datastream at the output 14 of the means 10 for generating an encrypted datastream does not differ from the data stream syntax determined by theencoder 16. The influencing by the encryption means 18 especiallyincludes changing the encoder internal data 20 a and/or the output dataof the encoder 20 b in an uniquely reversible way based on a key,leading to the fact that the encrypted data stream generated at theoutput 14 differs concerning its payload information from the payloadinformation of a data stream that would be generated by the encoder 16(by the means 10, respectively) if it were not subjected to aninfluencing by the encryption means 18.

As already mentioned, the encoder 16 according to a preferred embodimentof the present invention is arranged as an audio encoder according tothe standard MPEG layer-3 or according to the standard MPEG-2 AAC.However, the same could also be an audio encoder without entropyencoding like, for example, according to the standard MPEG layer-2.Apart from that, the encoder 16 could also be an encoder for voicesignals that carries out no encoding in the frequency range, but anencoding in the time domain, by using, for example, prediction or vectorquantization techniques. The encoder 16 could, of course, also be avideo encoder compressing video input data in order to enable atransmission of those data via bandwidth limited transmission channels.

The encoder 16 can thus be any encoder converting input data intoencoded output data according to set regulations wherein the data streamsyntax of the output data is defined by the encoder. Usually, a decoderexists for every encoder, in such a way that the encoded data stream canbe decoded again. However, this still means that each encoder, willgenerate a data stream with a predefined data stream syntax that has tobe predefined that a decoder that is mostly complementary to the encodercan decode the encoded data stream. However, this is only possible whenthe decoder can understand or interpret the data stream syntax of theencoded data stream. Therefore, a predefined data stream syntax can beassigned to each encoder for which a decoder exists.

FIG. 2 shows a schematic block circuit diagram of an inventive apparatus30 for generating a decrypted data stream. It comprises an input 32 andan output 34. A decoder 36 is connected between the input 32 and theoutput 34, the decoder being arranged for a predefined data streamsyntax determined by the encoder 16 (FIG. 1) and that is not touched bythe encryption means 18 (FIG. 1) according to the invention in such away that the data stream at the output 14 of the apparatus 10 forgenerating an encrypted data stream has the same data stream syntax asthe data stream at the input 32 of the apparatus 30 for generating adecrypted data stream.

The apparatus 30 for generating a decrypted data stream is essentiallycomplementary to the apparatus for generating an encrypted data stream10 in such a way that it also comprises a decryption means 38 apart fromthe decoder 36, which is again coupled to the decoder 36 in order toinfluence input data into the decoder 36 (branch 40 a) or decoderinternal data (branch 40 b) based on the key used in encrypting in sucha way that the changes introduced by the means 10 for generatingencrypted data streams that have been uniquely reversible changes can bereversed in order to obtain a decoded and un-encrypted data stream atthe output 34.

The inventive concept will be illustrated with the example of an audioencoder according to FIGS. 1 and 2. In this case, a time-discrete audiosignal is applied at the input 12 of the apparatus 10 for generating anencrypted data stream, that will be encoded by the encoder 16 and thatwill be output at the output 14 of the apparatus for generating anencrypted data stream as a bit stream having the same bit stream syntaxas predefined for the encoder 16 that has, however, been encrypted dueto the encryption means 18 and especially due to the interference of thedata via the branches 20 a and 20 b. The encrypted encoded bit streamwill be input into the input 32 of the apparatus 30 for generating adecrypted data stream and decoded again by the audio decoder 36 in orderto again obtain the time-discrete audio signal at the output 34. If theapparatus 30 is authorised for generating a decrypted data stream, i.e.,if it knows the key used by the encryption means 18, it will reverse theencryptions via the branches 40 a to 40 c in such a way that thetime-discrete audio signal at the output 34 of the apparatus 30 forgenerating a decrypted data stream will be an audio signal with fullaudio quality. However, if the apparatus 30 is not authorised, i.e., ifit does not know the used key, the time-discrete audio signal at theoutput 34 will be an audio signal that differs depending on theapplication more or less from the audio signal at the input 12 of theapparatus 10. If the data influencing by the encryption means has onlybeen limited, the time-discrete audio signal at the output 34 of theapparatus 30 for generating a decrypted data stream provides a certainaudio impression for the non-authorised user that might motivate him toobtain the authorisation, i.e., the key that the encryption means 18 hasused, to purchase it in order to obtain the full enjoyment.

Before several preferred embodiments of the present invention will bediscussed referring to FIGS. 3 to 9, first, a known encoding conceptwill be described referring to FIG. 10 and a known decoding conceptreferring to FIG. 11.

FIG. 10 shows a block circuit diagram for a known audio encoder that is,for example, arranged according to the standard ISO/IEC 13818-7 (MPEF-2AAC). The same comprises an audio input 200 and a bit stream output 202.A time-discrete audio signal at the audio input 200 is fed into ananalysis filter bank 204 in order to be mapped into the frequency range,such that a set of spectral values will result at the output of theanalysis filter bank representing the short-term spectrum of the audiosignal at the input 200, i.e., a block of time-discrete audio signalsamples is converted into a block of spectral values, i.e., into aspectral representation, by the analysis filter bank 200. These spectralvalues will be quantized in a block 206 referred to as quantizationconsidering a physcho-acoustic model 208 in such a way that a bit savingquantization is achieved but that the introduced quantization noise willbe below the masking threshold of the audio signal at the input 200, sothat it remains inaudible.

It is, therefore, a lossy quantization (generally a lossy encoding) thatdoes, however, not lead to irritating audio influences. The quantizedspectral values 206 will be subjected to an entropy encoding in a block210 in order to achieve further data compression. The entropy-encodedquantized spectral value will finally be lead into a bit streammultiplexer 212 that adds the corresponding side information to theentropy-encoded quantized spectral values according to the predefinedencoder syntax, such that an encoded bit stream will be output at thebit stream output 202, that has main information as payload informationin the shape of the entropy-encoded quantized spectral values and sideinformation in the shape of side information, like scale factors, etc.For further details to the single encoding blocks shown in FIG. 10 orregarding further blocks not shown there, like, for example, blocks forprocessing stereo signals, etc., please refer to the standard ISO/IEC13818-7 (MPEG-2 AAC). This standard further comprises a detailedillustration of the entropy encoding carried out in block 210. It shouldbe noted that the inventive concept can also be used with an encoderwithout entropy encoding (MPEG layer-1 and layer-2) and, in general,with any encoder generating an encoded data stream with a predefineddata stream syntax. For the present invention, it is especially notrelevant how the conversion of the time data into the spectral data willbe achieved, the same can therefore also be applied to the so-calledsub-band encoders (for example, MPEG-1).

FIG. 11 shows a decoder complementary to FIG. 10 that is also carriedout by the AAC-standard. The same comprises a bit stream input 220coupled with a bit stream demultiplexer 222 carrying out ademultiplex-operation complementary to the bit stream multiplexer 212(FIG. 10) in order to, among other things, feed entropy-encodedquantized spectral values into an entropy decoding means 224 thatreverses the entropy encoding introduced in block 210 (FIG. 10). The nowonly quantized spectral values will be subjected to an inversequantization in a block 226 that is complementary to the operationcarried out in block 206. The now again re-quantized spectral valueswill again be converted from the spectral representation into the timelyrepresentation in the synthesis filter bank 228 in order to achieve atime-discrete audio signal at an audio output 230.

Referring to FIG. 1, it has been stated above that the inventiveapparatus for generating an encrypted data stream as it is illustratedschematically in FIG. 1, can influence encoder internal data via branch20 a and/or output data of the encoder 16 via branch 20 b. This will bediscussed referring to the known encoder that is exemplary illustratedin FIG. 10. Input data for the encoder are time-discrete audio signals.

The branch 20 a shown in FIG. 1 refers to encoder internal data. It canbe seen from FIG. 10 that encoders can be constructed from a pluralityof subsequent blocks wherein, in principle, all input and output data ofa block can be influenced in a uniquely reversible manner in order toobtain an encryption without changing the bit stream syntax. Controldata, like, for example, control data for the analysis filter bank 204,the quantization 206, the entropy encoding 210, etc., can be influencedin exactly the same way. Encoder internal data are therefore not onlythe actual payload data, i.e., the more or less processed spectralvalues, but also the control data that usually appear as sideinformation in the encoded bit stream. Finally, output data of theencoder, i.e., at the output of the bit stream multiplexer 212, can beinfluenced without changing the bit stream syntax. In the easiest case,entropy encoded words could, for example, be resorted, i.e., scrambled.The code words can, of course, already be scrambled directly before thebit stream multiplexer in a uniquely reversible manner based on a key,whereby it becomes clear that it is, in principle, irrelevant, whetherinput data of the encoder from FIG. 10, encoder internal data or outputdata of the encoder are influenced by the encryption means 18 (FIG. 1).

It should be noted here that scrambling of single bits of entropy codewords can lead to a destruction of the data stream syntax, since Huffmancode words have, for example, a different length and an entropy decoderconfronted with bit-by-bit scrambled code words can very likely not workcorrectly any more, since it is not able to find the correct beginningor the correct end of a code word as the data stream syntax within thecode words is disturbed.

In the following, reference will be made to FIG. 3 in order to explain apreferred embodiment of the present invention for the apparatus 10 forgenerating an encrypted data stream. In FIG. 3 as well as in thefollowing Figs., same elements have the same reference numbers.Especially, the blocks described referring to FIGS. 10 and 11 have thesame reference numbers.

FIG. 3 shows a preferred embodiment where the encryption means 18 merelyinfluences encoder internal data, i.e., entropy encoded quantizedspectral values. It performs this by using a scrambling means in such away that entropy encoded quantized spectral values represented by codewords will for example be repositioned, i.e., resorted depending on akey k. That way, always two adjacent code words could be interchanged.This would lead to significant quality impairments in the decoded audiosignal, but not to the fact that a user would obtain no impression ofthe audio signal at all. The scrambling means 180 could, however, justas well act on the side information like, for example, scale factorsdepending on the user key k. If entropy-encoded quantized spectralvalues are merely resorted like in the embodiment shown in FIG. 3, nochange of the length of the encrypted data stream at output 14 of theencryption apparatus 10 will occur, such that the encoded encrypted datastream fits into the same transmission channel as the non-encrypteddecoded data stream.

A further preferred embodiment is shown in FIG. 4 where the scramblingmeans 180 is connected between the entropy encoder 210 and the quantizer206. In the easiest case, quantized spectral values that have not yetbeen entropy encoded, are scrambled here. This means that contrary toFIG. 3, the scrambled quantized spectral values will now be entropyencoded.

In the following, a generally known scrambling function, which iscarried out as a so-called “Seed-Generating” algorithm, will bedescribed merely exemplary. Here, a random number generator is usedwhich detects a random number sequence depending on a certain startvalue, i.e., the seed. The significance about this is that the randomnumber generator will provide the same random number sequence again andagain if it gets the same start value, it will, however, result in adifferent random number sequence if it gets a different start value. Inthis example, the start value would be the key k. The quantized spectralvalues (in FIG. 4) can now be linked bit-by-bit with a pseudo random bitsequence via, for example, a XOR function. Thereby, certain bits of thequantized spectral values will be changed, what represents an encryptionthat can only be reversed by an apparatus for generating a decrypteddata stream comprising the same key, i.e., the same start value for itsrandom number generator that again carries out a XOR link of thequantized spectral values with the scrambled quantized spectral values,as it will be shown in more detail below. It should be noted that theXOR link is only an example for an uniquely reversible change. The XORfunction has the advantage that a double application of the samefunction leads back to the starting point such that only one singlefunction and not a first function and a second inverse function have tobe implemented. In principle, every reversible function can be used forlinking.

If the encryption means does not influence all the bits of a quantizedspectral value, but only the least significant bits, the encryption willbe “softer” in such a way that the encrypted audio stream has only beeninfluenced in a limited manner and will still have a relatively goodaudible quality. Thus, it can be seen that the intensity of theencryption according to the present invention can be adjusted almostarbitrarily. If a very massive encryption is desired, it is possible toinfluence the scale factors directly. In certain encoding methods, theycarry, however, the significant intensity information, which is whyinfluencing the scale factors can lead to very significant impairmentsof the audio quality.

In the above, a simple mode of operation of the encryption means 18 withthe scrambling means 180 has already been described. If influencing ofthe quantized spectral values is already carried out before the entropyencoding, this will very likely lead to a changed length of the bitstream at the output 14 of the apparatus 10, since the quantizedspectral values changed bit-by-bit, will very likely bring aboutdifferent code words with differing lengths than the unscrambledspectral values that would be generated by the encoder 16 if noencryption means 18 were present. However, if the code words are merelyresorted after entropy encoding 210, as it is shown in FIG. 3, this willnot lead to a larger length of the bit stream at the output 14.

However, many further possibilities exist for influencing encoderinternal data. In audio encoders according to the AAC standard describedat the beginning, an entropy encoding is carried out that is referred tothere as “Noiseless Coding”. This is used to further reduce theredundancy of the scale factors and the quantized spectrum of each audiochannel. A Huffman encoding method is used as entropy encoding method.Especially, for certain sections that can consist of several scalefactor bands, respective code tables (code books) are used. Especially,11 different normalised code tables exist that can each be uniquelyidentified by a code table number. Thus, the entropy encoder 210associates the respective code table number, to each section that isentropy encoded with the same code table. The scrambling means 180 couldnow already change the code table number. However, this change is onlypossible within a limited scope in order to achieve a reversible changewithin the bit stream syntax. In this way, code tables exist that canrepresent signed or unsigned n-tupels of quantized spectral values.Above that, code tables exist that are four-dimensional or twodimensional. This means that a code word represents four quantizedspectral values in the case of a four dimensional code table or twoquantized spectral values in the case of a two dimensional code table.

Some code tables represent a signed entropy encoding of spectral values,while other code tables represent an unsigned encoding of spectralvalues. If the code tables encode unsigned, the code word is immediatelyfollowed by a sign bit for each spectral value in the bit stream if therespective spectral value is not zero. A decoder can then decode thequantized spectral value again due to the Huffman code word and thefollowing sign bit. The encryption means 18 is adjusted in a preferredembodiment of the present invention to carry out a sign change of thequantized spectral values that are encoded with unsigned code tables.The sign change happens by changing the described sign, wherein thischange could either be carried out according to a certain pattern or byusing an XOR link of a pseudo random bit sequence with the sign data.This way, always the same length of the resulting bit streams will beachieved if only those quantized spectral values will be influenced thatare entropy encoded with unsigned code tables.

As already mentioned, in the AAC standard, one section, i.e. a certainfrequency band of the short-term spectrum of the audio signal that hasat least one scale factor band is entropy encoded with the same codetable. If the scrambling means 180 is designed such that it merelycarries out a resorting of the quantized spectral values in itsfrequency raster without carrying out changes to the quantized spectralvalue, a same length of the output side bit stream at the output 14 ofthe apparatus 10 for generating an encrypted data stream can beachieved. This is only true, when the resorting takes place only withinspectral areas where the encoding of the quantized spectral values iscarried out with the same type of entropy encoding, for example, thesame Huffman code book.

An identical length of the encrypted encoded data stream will further beachieved if in the case of using more dimensional code tables instead ofsingle quantized spectral values n-tupel of spectral values are resortedtogether.

Thus, an encoded encrypted data stream is generated at the output 14 ofthe apparatus 10 for generating an encrypted data stream having the samedata stream syntax as it is predetermined for, or by, the encoder 16 andthat has, above that the same length as a non-encrypted encoded datastream in especially preferred embodiments of the present invention.

Corresponding apparatuses 30 for generating a decrypted audio and/orvideo signal are illustrated in FIGS. 5 and 6. This way, the apparatus30 outlined in FIG. 5 is complementary to the apparatus for generating adecrypted data stream in FIG. 3 Analogous, the apparatus 30 forgenerating a decrypted audio and/or video signal illustrated in FIG. 6is complementary to the apparatus 10 for generating an encrypted datastream illustrated in FIG. 4. The decryption means 38 in FIGS. 5 and 6comprises a means 380 for carrying out an inverse scrambling(descrambling) in order to reverse the influences of the encoderinternal data, i.e., the entropy encoded quantized spectral values orthe quantized spectral values not yet entropy encoded, introduced by thescrambling means 180 (FIG. 3, FIG. 4).

Basically, it can be said that the function of the means 380 for inversescrambling is always complementary to the corresponding means 180 forscrambling. The use of a seed generating algorithm, i.e., akey-controlled pseudo random bit sequence, allows the means 180 and thecorresponding means 380 to be constructed in exactly the same way andthe key for encrypting to correspond exactly to the key for decrypting.Other solutions wherein the encryption means 180 and the decryptionmeans 380 are constructed differently and where the keys for encryptingand decrypting are not identical, but in a certain (context to oneanother can also be employed as long as the encryption means carries outuniquely reversible changes to the respective data based on the key andthe apparatus for generating a decrypted audio and/or video signal canreverse the introduced changes based on the key.

While preferred embodiments of the present invention for generating anencrypted data stream at the output 14 that generates the encrypted datastream at the output 14 from a time-discrete audio signal at the input12 have been described referring to FIGS. 3 and 4, an inventiveapparatus for generating e data stream according to another embodimentof the present invention that generates the encrypted data stream at itsoutput not from a time-discrete input signal, but from a differentlyencrypted (encoded) data stream will now be described referring to FIG.7

The apparatus 70 for generating an encrypted data stream shown in FIG. 7generates a data stream encrypted and encoded with a key k2 at itsoutput 72, while it receives a data stream encrypted and encoded with akey k1 differing from k2 at its input 74. Now, the apparatus 70 does notany longer generate an encrypted data stream from a time-discrete audioinput signal but, in general, a data stream encrypted with another keyfrom a data stream encrypted with a first key. Differing from FIG. 1,the apparatus 70 comprises an encryption means 18 and a partial encoder16′. The apparatus 70 further comprises a decryption means 38 and apartial decoder 36′. Contrary to the embodiments described in FIGS. 3and 4, the partial decoder 36′ only consists of a bit streamdemultiplexer 222 and an entropy decoder 224, while the partial encoder16′ now merely consists of an entropy encoder 210 and a bit streammultiplexer 212. The encryption means 18 shown in FIG. 7 influences theinput data of the partial encoder 16′, while analogous the decryptionmeans 38 of FIG. 7 influences the output data of the partial decoder 36.The output data from the partial decoder are the decoder internal data,i.e., the data that have been originally influenced in generating theencrypted data stream fed into the means 70 according to the previousterminology. Analogous, the input data into the partial encoder of theapparatus 70 are the encoder internal data of the encoder that hasoriginally generated the encrypted encoded data stream at the input.

In the following, the mode of operation of the apparatus 70 forgenerating an encrypted data stream shown in FIG. 7 will be discussed.At the input 74, the apparatus 70 receives an encoded data streamencrypted with a key k1 that has been encrypted in the embodiment shownhere in such a way that the quantized spectral values have beenscrambled before the entropy encoding or, in general, have, in some way,been influenced based on the key k1 in a reversible manner. At theoutput of the entropy decoder 224, the entropy-decoded quantizedspectral values that are still encrypted are present that will bedecrypted by the decryption means 38 based on the key k1 by using themeans 380 for carrying out an inverse scrambling in such a way thatbetween the part 30′ and the part 10′ a decoded data stream will bepresent that is now, however, no time-discrete audio and/or video signalor something similar, but comprises quantized spectral values, i.e.,encoder internal or decoder internal data, in the embodiment shown inFIG. 7. The quantized spectral values will be fed into the encryptionmeans 18 and, especially, into the scrambling means 180 in such a waythat they will be scrambled or, in general, influenced based on a key k2different to key k1 in order to then be entropy encoded in the partialencoder 16′, so that, finally an encoded data stream encrypted with keyk2 will result at the output 70. As it can be seen from FIG. 7 that thisis a so-called “Scrambling Transcoder”, i.e., a bit stream converterthat converts a bit stream encrypted with a key k1 directly into a bitstream with the key k2. The same no longer comprises a full audiodecoder or audio encoder, but merely certain parts of those that arecalled partial decoder or partial decoder in the sense of thisinvention.

FIG. 8 shows a general representation of an apparatus 70′ for generatingan encrypted encoded data stream that differs only from the apparatusshown in FIG. 7 in that the bit stream at the input 74′ is an encodednon-encrypted data stream that will be decoded by the partial decoder36′ and then by the partial encoder and will then be encoded andencrypted by the partial encoder 16′ in connection with the encryptionmeans 18 in such a way that an encrypted/encoded data stream will resultat output 72′. The apparatus 70′ shown in FIG. 8 could, for example, beused to convert a standard bit stream with the predefined data streamsyntax directly into a data stream encrypted with a certain key, whereinboth data streams have the predefined data stream syntax.

FIG. 9 shows another embodiment of an inventive apparatus 80 forgenerating a decrypted data stream with an output 82 and an input 84. Anencoded/encrypted data stream is fed into the input 84 which isdecrypted by using the means 38 coupled with the partial decoder 36, sothat a decoded decrypted data stream will result, that will again be fedinto a following partial encoder 16 in such a way that anencoded/non-encrypted data stream results. The apparatus 80 forgenerating an encrypted data stream illustrated in FIG. 9 is thus a bitor data stream converter converting a bit stream encrypted with a key k1directly into a standard bit stream, i.e., into a bit stream that isnon-encrypted and has the predefined data stream syntax.

Differing from the described embodiments for the apparatuses 70, 70′ and80, all influencing of encoder internal data described in thisapplication can be carried out in all described ways. Regarding theabove, it is obvious that the partial encoder and the partial decoder,respectively, can be adjusted to the corresponding influencing. If, forexample, a resorting of Huffman code words has been carried out, apartial decoder could merely contain a bit stream demultiplexer, whilethe partial encoder then only comprises a bit stream multiplexer.

1. Apparatus for generating an encrypted data stream from an audiosignal, comprising: an encoder encoding the audio signal in order togenerate a data stream with a predefined data stream syntax as outputsignal; an encryptor coupled with the encoder influencing encoderinternal data in a uniquely reversible manner based on a key such thatthe generated encrypted data stream comprises payload informationdiffering from payload information of a data stream that would begenerated by the apparatus without the presence of the encryptor andthat the generated encrypted data stream comprises the predefined datastream syntax, wherein said encoder is an encoder for audio signals,comprising: an analysis filter bank converting the audio signal from thetime domain into a spectral representation in order to obtain spectralvalues; a quantizer quantizing the spectral values under considerationof a psychoacoustic model; and an entropy encoder arranged to carry outan entropy encoding of the quantized spectral values via a plurality ofpredefined code tables wherein each code table for the entropy encodingof quantized spectral values is provided in a frequency band and whereinat least one frequency band comprises two or more quantized spectralvalues, and wherein said encryptor is arranged to resort the two or morequantized spectral values in the frequency band comprising two or morequantized spectral values having an associated code table based on thekey.
 2. Apparatus according to claim 1, wherein said encryptor isfurther arranged to resort the two or more quantized spectral valuesbased on the key such that the encoded data stream has the same bitlength as a data stream that would be generated by said apparatuswithout the presence of said encryptor.
 3. Apparatus according to claim1, wherein the encryptor is arranged in order to resort the two or morequantized values merely so strongly based on the key that the payloadinformation of the encrypted data stream differs only so strongly fromthe payload information of a data stream that would be generated withoutthe presence of the encryptor that a decoder that does not possess thekey provides a decoded output signal based on the encrypted data with aquality that is lower than the quality that the decoder would provide ifhe possessed the key, wherein however, a minimum quality is ensured. 4.Apparatus according to claim 1, in which the quantizer is arranged forgenerating the spectral values as main information and scale factors asside information each of which is associated to at least one quantizedspectral value; and in which said encryptor is further arranged toinfluence the scale factors generated by said quantizer based on thekey.
 5. Apparatus according to claim 1, wherein said encryptor isarranged to link the quantized spectral values in the frequency band,which includes two or more spectral values with a pseudo random bitsequence generated based on the key as start value via anEXCLUSIVE-OR-link.
 6. Apparatus according to claim 1, wherein merelyleast significant bits of spectral values are linked with a pseudorandom bit sequence.
 7. Apparatus according to claim 1, wherein saidquantized spectral values are signed and wherein said encryptor isfurther arranged to change the signs of quantized spectral values basedon the key.
 8. Apparatus according to claim 1, wherein said entropyencoder is arranged such that it comprises at least one code table whichis an unsigned code table such that a sign for a code word from the codetable is written separately from the code word into the payloadinformation, wherein said encryptor is further arranged to change thesign of at least one quantized spectral value based on the key beforesaid entropy encoding of said quantized spectral values.
 9. Apparatusaccording to claim 1, wherein at least one code table of the pluralityof code tables is a multidimensional code table, wherein a code wordrepresents a plurality of quantized spectral values, wherein saidencryptor is arranged to resort groups of quantized spectral values,wherein one group of spectral values has so many quantized spectralvalues as encoded by a code word of said multidimensional code table.10. Apparatus according to claim 1, wherein said encoder has a pluralityof sub-blocks connected with a bit stream multiplexer multiplexing thedata output from the single sub-blocks according to the predefined datastream syntax in order to obtain the output data of said encoder. 11.Apparatus for generating a second data stream encrypted based on asecond key from a first data stream encrypted based on a first key,wherein said first data stream is an audio signal encoded by using anencoder with a predefined data stream syntax, wherein said first datastream is encrypted such that two or more quantized spectral values in afrequency band comprising two or more quantized spectral values andhaving an associated code table have been scrambled based on the firstkey, wherein after the scrambling an entropy encoding of the quantizedspectral values has been carried out via a plurality of predefined codetables, wherein each code table is provided for the entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,wherein the scrambling comprises resorting the spectral values onlywithin spectral areas having the same codebook associated therewith,comprising: a partial decoder reversing part of the encoding such thatthe scrambled two or more spectral values are present; a decryptordecrypting the scrambled two or more spectral values by reversing thescrambling based on the first key, wherein the reversing the scramblingcomprises resorting the spectral values only within spectral areashaving the same codebook associated therewith; an encryptor influencingthe sequence of the two or more spectral values of the frequency bandthat has an associated code table based on the second key, wherein theinfluencing the sequence comprises resorting the spectral values onlywithin spectral areas having the same codebook associated therewith; apartial encoder carrying out part of the encoding that has been reversedby the partial decoder in order to generate the second data streamencrypted based on the second key, wherein the second data stream hasthe predefined data stream syntax.
 12. Apparatus for generating a seconddata stream encrypted based on a key from a first data stream, whereinsaid first data stream is an audio signal encoded using an encoder witha predefined data stream syntax, comprising: a partial decoder reversingpart of the encoding such that quantized spectral values of the audiosignal are present; an encryptor scrambling two or more quantizedspectral values in a frequency band comprising two or more spectralvalues based on the first key, wherein one of a plurality of predefinedcode tables is associated to the frequency band for the entropyencoding, wherein each code table is provided for an entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,wherein the encryptor is arranged to scramble the quantized spectralvalues that have the same associated code table, wherein the scramblingcomprises resorting the quantized spectral values only within spectralareas having the same codebook associated therewith; a partial encodercarrying out part of the encoding that has been reversed by the partialdecoder in order to generate the data stream encrypted based on the key,wherein the second data stream has the predefined data stream syntax.13. Apparatus for generating a decrypted second data stream from a firstdata stream encrypted based on a key, wherein said first data stream isan audio signal with a predefined data stream syntax encoded by using anencoder, wherein said first data stream is encrypted such that at leasttwo or more quantized spectral values in a frequency band have beenscrambled based on the first key, wherein a plurality of predefined codetables for an entropy encoding is associated with the frequency bandwhose quantized spectral values have been scrambled, wherein each codetable for the entropy encoding is provided for the entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,wherein the scrambling comprises resorting the quantized spectral valuesonly within spectral areas having the same codebook associatedtherewith, comprising: a partial decoder reversing part of the encodingsuch that the scrambled two or more quantized spectral values arepresent, wherein the scrambled two or more quantized spectral valuesbelong to a frequency band that has an associated code table; adecryptor decrypting the scrambled two or more quantized spectral valuesby reversing the scrambling based on the key, wherein the reversing thescrambling comprises resorting the quantized spectral values only withinspectral areas having the same codebook associated therewith; a partialencoder carrying out part of the encoding that has been reversed by thepartial decoder in order to generate the second data stream with thepredefined data stream syntax.
 14. Apparatus according to claim 11,wherein said partial decoder has a bit stream demultiplexer, whereinsaid encoder internal data are the output data from the bit streamdemultiplexer.
 15. Apparatus according to claim 14, wherein said partialdecoder further comprises an entropy decoder following the bit streamdemultiplexer, wherein said encoder internal data are the output datafrom the entropy decoder.
 16. Apparatus according to claim 11, whereinscale factors are influenced apart from the two or more quantizedspectral values.
 17. Apparatus for generating a decrypted audio signalfrom an encrypted data stream comprising quantized spectral values of anaudio signal being scrambled and afterwards entropy encoded within afrequency band in a uniquely reversible manner, wherein the frequencyband is defined that it has an associated code table from a plurality ofcode tables for the entropy encoding, wherein the encrypted data streamcomprises payload information differing from payload information of anon-encrypted data stream and wherein said encrypted data streamcomprises a data stream syntax similar to a data stream syntax of anon-encrypted data stream, wherein the scrambling comprises resortingthe quantized spectral values only within spectral areas having the samecodebook associated therewith, comprising: a decoder decoding input datain order to generate decoded output data, wherein the decoder comprisesan entropy decoder for reversing the entropy encoding in order to obtainthe scrambled quantized spectral values; and a decryptor influencing thescrambled spectral values based on a key by reversing the uniquelyreversible scrambling which has been carried out in an apparatus forgenerating an encrypted data stream in order to obtain the decryptedaudio and/or video signal, wherein the reversing the scramblingcomprises resorting the quantized spectral values only within spectralareas having the same codebook associated therewith.
 18. Apparatusaccording to claim 17, wherein said decoder further comprises: aplurality of functional blocks coupled with a bit stream demultiplexerconducting parts of the data stream to the single blocks according tothe predefined data stream syntax.
 19. Apparatus according to claim 18,wherein said decoder further comprises: a synthesis filter bank in orderto convert a spectral representation of the audio signal into a timelyrepresentation.
 20. Method for generating an encrypted data stream froman audio signal, comprising: encoding the audio signal in order togenerate a data stream with a predefined data stream syntax as outputsignal; encrypting encoder internal data by influencing the same in auniquely reversible manner based on a key such that the generatedencrypted data stream comprises payload information differing frompayload information of a data stream that would be generated without thestep of encrypting and that the generated encrypted data streamcomprises the predefined data stream syntax, wherein in the step ofencoding an audio signal is encoded, comprising: converting the audiosignal from the time domain into a spectral representation in order toobtain spectral values; quantizing the spectral values underconsideration of a psychoacoustic model; and entropy encoding of thespectral values via a plurality of predefined code tables wherein eachcode table for the entropy encoding of quantized spectral values isprovided in a frequency band and wherein at least one frequency bandcomprises two or more quantized spectral values, and wherein said stepof encrypting is carried out to scramble the two or more quantizedspectral values in the frequency band comprising two or more quantizedspectral values having an associated code table based on the key. 21.Method for generating a second data stream encrypted based on a secondkey from a first data stream encrypted based on a first key, whereinsaid first data stream is an audio signal with a predefined data streamsyntax encoded by using an encoder, wherein said first data stream isencrypted such that two or more quantized spectral values in a frequencyband comprising two or more quantized spectral values and having anassociated code table have been scrambled based on the first key,wherein after the scrambling an entropy encoding of the quantizedspectral values has been carried out via a plurality of predefined codetables, wherein each code table is provided for the entropy encoding ofquantized spectral values in a frequency band and wherein at least onefrequency band comprises the two or more quantized spectral values,wherein the scrambling comprises resorting the spectral values onlywithin spectral areas having the same codebook associated therewith,comprising: reversing part of the encoding such that the scrambled twoor more spectral values are present; decrypting the scrambled two ormore spectral values by reversing the scrambling based on the first key,wherein the reversing the scrambling comprises resorting the spectralvalues only within spectral areas having the same codebook associatedtherewith; encrypting by influencing the sequence of the two or morespectral values of the frequency band that has an associated code tablebased on the second key, wherein the influencing the sequence comprisesresorting the spectral values only within spectral areas having the samecodebook associated therewith; carrying out the part of the encodingthat has been reversed by the step of reversing in order to generate thesecond data stream encrypted based on the second key, wherein the seconddata stream has the predefined data stream syntax.
 22. Method forgenerating a second data stream encrypted based on a key from a firstdata stream, wherein said first data stream is an audio signal with apredefined data stream syntax encoded by using an encoder, comprising:reversing part of the encoding such that quantized spectral values ofthe audio signal are present; encrypting by scrambling two or morequantized spectral values in a frequency band comprising two or morespectral values based on the first key, wherein one of a plurality ofpredefined code tables is associated to the frequency band for theentropy encoding, wherein each code table is provided for an entropyencoding of quantized spectral values in a frequency band and wherein atleast one frequency band comprises the two or more quantized spectralvalues, wherein the encryptor is arranged to scramble the quantizedspectral values that have the same associated code table, wherein thescrambling comprises resorting the quantized spectral values only withinspectral areas having the same codebook associated therewith; carryingout part of the encoding that has been reversed by the partial decoderin order to generate the data stream encrypted based on the key, whereinthe second data stream has the predefined data stream syntax.
 23. Methodfor generating a decrypted second data stream from a first data streamencrypted based on a key, wherein said first data stream is an audiosignal with a predefined data stream syntax encoded by using an encoder,wherein said first data stream is encrypted such that at least two ormore quantized spectral values in a frequency band have been scrambledbased on the first key, wherein a plurality of predefined code tablesfor an entropy encoding is associated with the frequency band whosequantized spectral values have been scrambled, wherein each code tablefor the entropy encoding of quantized spectral values is provided in afrequency band and wherein at least one frequency band comprises the twoor more quantized spectral values, wherein the scrambling comprisesresorting the quantized spectral values only within spectral areashaving the same codebook associated therewith, comprising: reversingpart of the encoding such that the scrambled two or more quantizedspectral values are present, wherein the scrambled two or more quantizedspectral values belong to the frequency band that has an associated codetable; decrypting the scrambled two or more quantized spectral values byreversing the scrambling based on the key, wherein the reversing thescrambling comprises resorting the quantized spectral values only withinspectral areas having the same codebook associated therewith; carryingout part of the encoding that has been reversed by the step of reversingin order to generate the second data stream with the predefined datastream syntax.
 24. Method for generating a decrypted audio signal froman encrypted data stream comprising quantized spectral values of anaudio signal being scrambled and afterwards entropy encoded within afrequency band in a uniquely reversible manner, wherein the frequencyband is defined by having an associated code table from a plurality ofcode tables for the entropy encoding wherein the encrypted data streamcomprises payload data differing from payload data of a non-encrypteddata stream and wherein the encrypted data stream comprises a datastream syntax similar to a data stream syntax of a non-encrypted datastream, wherein the scrambling comprises the spectral values only withinspectral areas having the same codebook associated therewith,comprising: decoding input data in order to generate decoded outputdata, wherein in the step of decoding an entropy encoding for reversingthe entropy encoding is carried out in order to obtain the scrambledquantized spectral values; and decrypting by influencing the scrambledquantized spectral values based on a key in order to reverse theuniquely reversible scrambling that has been carried out by generatingan encrypted data stream in order to obtain the decrypted audio signal,wherein the influencing comprises resorting the spectral values onlywithin spectral areas having the same codebook associated therewith. 25.Apparatus for generating an encrypted data stream from an audio signal,comprising: an encoder encoding the audio signal in order to generate adata stream with a predefined data stream syntax as output signal; anencryptor coupled with the encoder influencing encoder internal data ofthe encoder in a uniquely reversible manner based on a key such that thegenerated encrypted data stream comprises payload information differingfrom payload information of a data stream that would be generated by theapparatus without the presence of the encryptor and that the generatedencrypted data stream comprises the predefined data stream syntax,wherein said encoder is an encoder for audio signals, comprising: ananalysis filter bank converting the audio signal from the time domaininto a spectral representation in order to obtain spectral values; aquantizer quantizing the spectral values under consideration of apsychoacoustic model; and an entropy encoder arranged to carry out anentropy encoding of the spectral values in order to obtain a sequence ofcode words wherein the sequence of code words represents an entropyencoded version of the audio signal, and wherein said encryptor isarranged to scramble the sequence of code words by changing an order ofcode words based on the key.
 26. Apparatus according to claim 25,wherein said encryptor is arranged in order to scramble the code wordsbased on the key merely so strongly that the payload information of theencrypted data stream differs only so strongly from the payloadinformation of a data stream that would be generated without thepresence of the encryptor that a decoder that does not possess the keyprovides a decoded output signal based on the encrypted data with aquality that is lower than the quality that the decoder would provide ifhe possessed the key, wherein however, a minimum quality is ensured. 27.Apparatus according to claim 25, wherein always two adjacent code wordsare exchanged with each other.
 28. Apparatus for generating a seconddata stream encrypted based on a second key from a first data streamencrypted based on a first key, wherein said first data stream is anaudio signal with a predefined data stream syntax encoded using anencoder, wherein said first data stream is encoded such that a sequenceof code words generated by entropy encoding of quantized spectral valueshas been scrambled by changing an order of code words based on the firstkey, comprising: a partial decoder reversing part of the encoding suchthat the scrambled sequence of code words is present; a decryptorreversing the scrambling based on the first key, wherein the reversingthe scrambling comprises changing the order of code words in thescrambled sequence; an encryptor scrambling the sequence of code wordsbased on the second key by changing an order of code words; a partialencoder carrying out part of the encoding that has been reversed by thepartial decoder in order to generate the second data stream encryptedbased on the second key, wherein the second data stream has thepredefined data stream syntax.
 29. Method for generating an encrypteddata stream from an audio signal, comprising: encoding the audio signalin order to generate a data stream with a predefined data stream syntaxas output signal; encrypting by influencing encoder internal data in thestep of encoding in a uniquely reversible manner based on a key suchthat the generated encrypted data stream comprises payload informationdiffering from payload information of a data stream that would begenerated by the apparatus without the presence of the encryptor andthat the generated encrypted data stream comprises the predefined datastream syntax, wherein the step of encoding comprises: converting theaudio signal from the time domain into a spectral representation inorder to obtain spectral values; quantizing the spectral values underconsideration of a psychoacoustic model; and entropy encoding thespectral values in order to obtain a sequence of code words wherein thesequence of code words represents an entropy encoded version of theaudio signal, and wherein in said step of encrypting based on the keythe sequence of code words is scrambled by changing an order of codewords.
 30. Method for generating a second data stream encrypted, basedon a second key from a first data stream encrypted based on a first key,wherein said first data stream is an encoded audio signal with apredefined data stream syntax, wherein said first data stream isencrypted such that a sequence of code words generated by entropyencoding quantized spectral values has been scrambled by changing anorder of code words based on the first key, comprising: reversing partof the encoding such that the scrambled sequence of code words ispresent; reversing the scrambling based on the first key, wherein thereversing the scrambling comprises changing the order of code words inthe scrambled sequence; encrypting by scrambling the sequence of codewords based on the second key, wherein the scrambling comprises changingthe order of code words in the sequence; carrying out part of theencoding that has been reversed in the step of reversing in order togenerate the second data stream encrypted based on the second key,wherein the second data stream has the predefined data stream syntax.